In a liquid crystal display device, a classification based on an operating mode for liquid crystal molecules includes modes such as PC (phase change), TN (twisted nematic), STN (super twisted nematic), ECB (electrically controlled birefringence), OCB (optically compensated bend), IPS (in-plane switching), VA (vertical alignment), FFS (fringe field switching) and FPA (field-induced photo-reactive alignment). A classification based on a driving mode in the device includes PM (passive matrix) and AM (active matrix). The PM is classified into static, multiplex and so forth, and the AM is classified into TFT (thin film transistor), MIM (metal-insulator-metal) and so forth. The TFT is further classified into amorphous silicon and polycrystal silicon. The latter is classified into a high temperature type and a low temperature type depending on the production process. A classification based on a light source includes a reflection type utilizing natural light, a transmission type utilizing a backlight and a semi-transmission type utilizing both natural light and a backlight.
The liquid crystal display device includes a liquid crystal composition having a nematic phase. This composition has suitable characteristics. An AM device having good characteristics can be obtained by improving the characteristics of this composition. Table 1 below summarizes the relationship between two characteristics. The characteristics of the composition will be further explained on the basis of a commercially available AM device. The temperature range of a nematic phase relates to the temperature range in which the device can be used. A desirable maximum temperature of the nematic phase is approximately 70° C. or higher and a desirable minimum temperature of the nematic phase is approximately −10° C. or lower. The viscosity of the composition relates to the response time of the device. A short response time is desirable for displaying moving images on the device. Response time that is one millisecond shorter than that of the other devices is desirable. Thus a small viscosity of the composition is desirable. A small viscosity at a low temperature is more desirable.
TABLE 1Characteristics of compositions and AM devicesNo.Characteristics of compositionsCharacteristics of AM devices1a wide temperature range ofa wide temperature range ina nematic phasewhich the device can be used2a small viscositya short response time3a suitable optical anisotropya large contrast ratio4a large positive or large negativea low threshold voltage anddielectric anisotropylow power consumption, alarge contrast ratio5a large specific resistancea large voltage holding ratio anda large contrast ratio6a high stability to ultravioleta long service lifelight or heat7a large elastic constanta large contrast ratio and a shortresponse time
The liquid crystal composition is prepared by mixing a liquid crystal compound having a large dielectric anisotropy and a liquid crystal compound having a small dielectric anisotropy. The dielectric anisotropy of the composition is increased by the former, and thus the threshold voltage of the device decreases. The maximum temperature of a nematic phase of the composition is increased or the minimum temperature of a nematic phase is decreased by the latter, and thus the temperature range in which the device can be used increases. The viscosity of the composition is decreased by the latter, and thus the response time of the device decreases.
A variety of liquid crystal compounds having a large positive or large negative dielectric anisotropy have been prepared until now. In contrast, a conventional compound is often used for a liquid crystal compound having a small dielectric anisotropy. Thus, we try to synthesize a new compound. This is because good physical properties that cannot be observed in the conventional compound are expected.
JP S57-165328 A (1982) discloses compound (A) in Example 25.

JP H08-048978 A (1996) discloses compound (B) in Example 7.

JP H05-320081 A (1993) discloses compound (C) in Example 1.

Compound (D) is disclosed in Proceedings of SPIE—The International Society for Optical Engineering (1998), 3319 (Liquid Crystals: Chemistry and Structure), 31-34.
